A lot more wind is lighting up American homes, courtesy of Washington, and believe it or not that's a little bit of a surprise.

As the government revised its estimate of fourth-quarter economic growth higher — from a 0.1% annual rate to 0.4% — Thursday, economists said a major reason was a previously unaccounted-for increase in spending late last year on wind farms. The growth was due partly to scrambling by developers to get projects completed before a tax credit expired at the end of the year.

The push wasn't included in the Commerce Department's first two estimates of fourth-quarter gross domestic product because the surge was first documented after the initial GDP estimates were released, said IHS Global Insight chief U.S. economist Nigel Gault.

Wind-power growth is likely to resume later this year, because Congress and President Obama extended the credit for only one year as part of the tax law approved in January.

"The level and timing of investment in wind energy is tied to tax incentives,'' Gault said. "So the expiry of a key tax credit led to a surge.''

The wind industry invested about $25 billion in new facilities last year and, along with its suppliers, employed about 75,000 people in late 2011, said Liz Salerno, director of industry data and analysis at the American Wind Energy Association.

The tax credit is worth 2.2 cents per kilowatt hour once the plant begins selling power. The average U.S. cost of residential electricity is about 10 cents per kilowatt hour. In states such as Texas, wind-based electricity can cost as little as 4 cents per kilowatt hour, according to the Energy Department.

"The fundamentals of wind have improved a lot, the technology is better,'' said Richard McMahon, vice president for energy supply and financing at the Edison Electric Institute, a trade association for utilities. "It probably doesn't revolve around tax policy anymore.''

The Commerce Department said investment in commercial structures rose at an annual rate of 16.7% in the fourth quarter — well above the 5.8% growth previously reported. Developers added 8,380 megawatts of wind-driven electricity capacity, bringing the U.S. total to 60,000 megawatts — enough to power 14.7 million homes.

Investment in power and communication structures, which include wind farms, accounted for about 80% of the gain in commercial construction.

Because of the scheduled expiration of the tax credit, many more projects that were not near completion were halted last year, prompting layoffs at suppliers, Salerno said.

They are resuming work, and more projects are being advertised by utilities that want to begin construction this year to take advantage of the one-year extension of the credit, she added.

Utilities will keep buying wind power after the credit expires, because most states are requiring utilities to boost the percentage of electricity made from renewable energy, and because the industry wants to hedge against potential increases in natural gas and coal prices, McMahon said.